The invention relates to centrifuging devices and to a method for controlling the acceleration thereof to a particular operating speed to prevent imbalance of the device exceeding a predetermined maximum. This is accomplished by controlling the temporal alteration of the rotational speed as the maximum permissible imbalance is approached.
In the acceleration of centrifuging devices, such as centrifuges or washing machines, imbalances frequently occur, which impose potentially unacceptable loads on the device, in particular its bearings. This is of particular significance in the case of centrifuging devices with a horizontal axis of rotation, for example the drums in washing or spinning machines, particularly those with large capacities. In such devices, on acceleration the product; e.g., the pieces of washing, is lifted by the rotating centrifuge drum, but detaches itself before the apex from the drum wall and falls in a free trajectory into the lower part of the drum. When the rotational speed is increased so much that the centrifugal force exceeds the gravitational force, the free trajectory disappears and the washing rests against the inner side of the drum. Depending on the distribution of the product; i.e., the washing, a certain imbalance results, which cannot be avoided even by careful packing of the product into the centrifuging device. In practice it is therefore necessary to limit the imbalance occurring on rotation of the centrifuging device at the final operation rotational speed to a permissible level.
According to German Patent Specification Nos: 29 15 815 or 30 39 315 in a centrifuging process the rotational speed is only increased to one at which the maximum permissible imbalance is reached. The dewatering capacity is thus limited. In German Patent Specification Nos: 22 04 325 or 29 39 340 it is proposed to measure the imbalances occurring in washing or centrifuging machines, and stop the device when the imbalance on acceleration exceeds a certain value, and subsequently to undertake one or more acceleration attempts until the design rotational speed is reached without the permissible imbalance being exceeded. However, such a method is time-consuming, and inefficient and expensive in terms of energy.
Reference is also directed to copending U.S. application Ser. No. 435,033, filed 10-18-82 in which it is proposed that, instead of switching off the centrifuging device when a particular imbalance threshold has been reached, simply to keep the rotational speed constant for a particular time. In so doing, utilization is made of the fact that the product, in particular the washing, begins to flow slowly and distributes itself more evenly over the inner wall of the drum. At the end of this pause period, in most cases the product has distributed itself so evenly that the acceleration process can be resumed without danger. Only if it is established that the imbalance has not been significantly or sufficiently reduced does the centrifuging device have to be switched off.
This technique results in a certain improvement in efficiency, but we have found that greater savings on time and energy can be achieved.